Manufacture of impregnated glass fiber tanks



March 28, 1961 c' M' NERW'CK 2,977,269

MANUFACTURE OF' IMPREGNATED GLASS FIBER TANKS Filed June 27, 1958 4Sheets-Sheet 1 F191 35 2o FIG. 5

ATTORNEYS March 28, 1961 c, M. NERwlcK MANUFACTURE OF' IMPREGNATED GLASSFIBER TANKS Filed June 27, 1958 4 Sheets-Sheet 2 ATTORNEYS March 28,1961 C, M NERwlcK MANUFACTURE OF IMPREGNATED GLASS FIBER rIANKS FiledJune 27, 1958 4 Sheets-Sheet 5 FIG. 7

INVENTOR. 8 CHARLES M. NERVWCK ATTORNEYS March 28, 1961 C- M' NERWCK2,977,269

MANUFACTURE OF IMPREGNATED GLASS FIBER TANKS Filed June 27, 1958 4Sheets-Sheet 4 gf/z' 1, l

FIG. 9 l` 60X y 60m@ VV? i FIG. I2

INVENTOR.

CHARLES IVI. /VERWICK MANUFACTURE or rMrRnGNArnn crass aman 'ranasCharles M. Nerwick, Willoughby, Ohio, assignor to Structlral Fibers,Inc., Chardon, Ohio, a corporation of hio Filed June'2'7, 1958, Ser. No.745,093

9 Claims. (Ci. 154-83) This invention relates to the manufacture offiberreinforced molded articles and, more particularly, to thefabrication of such articles by laying up porous, fibrous matsapproximately in the shape of the article to be produced andimpregnating them with a liquid Which `is subject to curing or settingby application of a setting agent such as heat, whereby a substantiallyhomogeneous seamless article is achieved.

The invention constitutes an improvement in the method described andclaimed in a copending application of Donald W. Randolph, Serial No.577,487, filed April 1l, 1956.

yDuring recent years the manufacture of fiber-reinforced molded articleshas been considerably stimulated because the balancev between materialcosts and fabricating costs on the one hand and utility, strength anddurability on the other hand has compared favorably with similarbalances made in connection with older and more conventional methods andproducts.

One vof the applications in which fiber-reinforced molded articles havelong shown promise is in the manufacture of domestic water softenertanks and similar large, water-tight, and chemically resistant, hollowobjects. However, progress in thisparticular field has been limitedbecause of high costs andother disadvantages inherent in the fabricationof several subassemblies prior-to final assembly and fabrication of thecompleted product. Attempts to form a large, integral one-piece unit ina single pressure molding or forming operation have not been successfuldue to the fugitive nature of fiber matting when it is confined andcompressed betweennarrowly spaced walls between which conventionalsettable liquid resins are forced under pressure. For example, whensections of fiber matting are layed up` in the approximate form of thedesired object and encased in orl backed up by an external rigid mold,between the mold surfaces and an expandable, iiuid-filled bag orenvelope, or other fiuid- 'expanded memberane, for defining the shape ofthe, finished article, and' thereupon an impregnating liquid is forcedthrough the matting to permeate it, the liquid acts as a lubricant, andthe sections of matting tend to flow with the liquid, destroyingthe-conformation of the layed- ,v

up matting. This problem has been particularly acute when the mattingemployed is made up of loosely felted, i

individual fibers (eg. glass fiber matting). Even though the fibers havebeen sprayed with a light coating of liquid resin adhesive during thefelting processrso as to hold them together without significantlydiminishing their porous loosely felted character, the individual fibersare by no means securely heldin place in the matting structure. As aresult, when the impregnating liquid is forced through such matting, theindividual fibers,` as `well as whole sections of fiber matting, tend tomigrate by liowing with the impregnating liquid.

These difficulties may be encountered when using felted fiber matting,alone or in combination with woven fiber matting or the like, eventhough an expandable bag,

envelope or other liexible mebrane Ais heldy ywith con- ICC siderablepressure against the matting as the impregnating liquid is forcedtherethrough. As the pressure used to hold the'matting in place againsta rigid mold surface'iis increased, the matting is compressed with aconsequent reduction in its porosity, and greaterpressures on theimpregnating liquid are required to force it through the matting at thesame rate. This pressure of thev impregnating liquid opposes the matholding effect of the increased membrane pressure, and the tendency ofthe individual fibers and the sections of fiber matting to migratepersists. In fact, wherea gas is used as the pressurizing medium formaintaining a relatively high compressing pressure on the matting, therelatively high pressure of the impregnat- Y sulting in the formationof-voids in the final product.

Such voids very seriously weaken the walls of the final product andrender it useless. If, because of a relatively high compressing pressureon the fiber matting, it becornes necessaryto .use avery high pressureto force the impregnating liquid through the matting at a practicalrate, the `tendency to trap air in the body of the product increases.This is due to the fact that the expressing of the impregnating liquidthrough the highly compressed matting does not progress uniformly, and.pocketsr containing air may be trapped between spaced apart, irregularlyflowing-streams of the resin and be surrounded with resin so that theair cannot escape. Thus, it is desirable to avoid such conditions byfinding` an expedient by which thematting may be held intact and inplace without placing it under too high a compressing pressure duringthe liquid impregnation step.

According to the present invention, one-piece, fiberreinforced, hollowtanks may be more vsuccessfully and economically pressure molded.Articles made according to the present invention are reinforcedthroughout with substantially evenly distributed matted fibers, in a`manner 'to be described below. `The entrapment of air and the formationof voids are eliminated. Wall thicknessof the ,final product issubstantially uniform. All portions of the In general, the presentinvention is similar to the v method disclosed,y and claimed in theaforementioned copending Randolph application, in which pressure issuitably applied to theV interior of the Ylayed-up form of vlibermatting by the introduction of a liquid winto 4a *flexible envelopesur-rounded by the matting and byv a rigid exterior mold. In the presentinvention, air or other gas is employed as the pressure applyingVmedium,

' instead of the liquid used by Randolph.' A' particularly nerandraisedftoa relatively high valuebefore introducing the settableresin, and is then relieved to a relatively low value duringintroduction of the settable resin. Each of these departures from theRandolph method produces distinct advantages describedhereinafter. Stillother signiicant departures from the Randolph method are the addition ofVa, resin-aerating step and a mold evacuating step, preferably justbefore introducing the settable resin, as also described hereinafter.

The invention reduces the cost of manufacturing large fiber-reinforcedhollow tanks and similar objects, and such tanks are produced'therebywhich are more useful and durable than those of the prior art.

The general objects of the present invention are to avoiddiscontinuities in the iber reinforcementk of the Vtank structure so asto provide a substantially uniform distribution of interlocked fiberstherethrough; to avoid air bubbles or pockets andv similardiscontinuities in the resin in which the reinforcing fibers areembedded so as to provide a reinforced resin mass of maximum strengthand minimum porosity; and to provide a high density of interlocked berreinforcement throughout the tank body.

More specic objects ofthe invention, by which it is particularlydistinguished from the method described and claimed in theaforementioned copending Randolph application, are: to achieve moreuniform compaction of the reinforcing fibers, particularly in theregions where the side walls of a tank or the like merges into the endWalls thereof; to reduce the amount of air entrained in the settableresin with which the reinforcing fibers are permeated; to more eectivelyeliminate air contained in the intersticial spaces of the ber mattingprior to its permeation with the resin; to speed up the fabricatingoperation and, as correlative benefits, to reduce the amount of heatthat must be supplied and obtain greater production from'the apparatus`and manpower required to carry out the method.

These and other objects and advantages of the linvention will becomeapparent from the following description of the invention, made by way ofexample. In the accompanying drawings which supplement the description:

Figure 1 illustrates, somewhat schematically, an initial or preparatorystep in the manufacture of fiber-reinforced hollow tanks according tothe herein described example of the invention.

Figure 2 illustrates the insertion of a roll of fiber matting into acylindrical mold section in a manner consistent with the practice of theherein described example of the invention.

Figure 3 is a view in cross-section of the top righthand portion ofmolding apparatus embodying the practice of the invention, the moldsections being parted and ber forms being inserted into place to besubsequently impregnated and molded according to the invention.

Figure 4 is a View similar to Figure 3, showing the lower right-handportion of apparatus embodying the practice of the invention.

Figure 5 is a cross-sectional View showing molding apparatus embodyingthe practice of the invention with al1 mold sections closed and with acentral expanding envelope almost fully expanded but with noresin as yetintroduced into the mold.

Figure 6 is a view similar to Figure 5 but more schematic in natureshowing apparatus embodying the practice of the invention just followingintroduction of resin into the mold.

Figure 7 is a view similar to Figure 6 showing apparatus embodying thepractice of the invention, following the'step ofcompressing the berwalls which have been laid up within the molding chamber and which -havebeen impregnated with resin.

Figure l8 is a perspective View of the lower end of suitable sealingring 29.

the tank showing a preferred foot construction on which the iinishedtank may rest.

Figure 9 is similar to Figure 1, but illustrates certain modificationsof the invention as applied to the manufacture of open end tubes insteadof closed end tanks.

Figure 10 is a plan view of a top mold closure plate for use in themanufacture of open end tubes.

Figure 11 is a plan view of a bottom mold closure plate for the samepurpose.

Figure l2 is a cross-sectional view of the mold, the end closure plates,and an interior expandable bag assembled to enclose the porous fiberform shown in Figure 9 for impregnation with resin.

The invention employs reinforcing fibers, such as glass fiber orequivalent material, suitably preformed into felted, woven, or otherwiseinterlocked mats or sheeting and shaped to conform to all or a portionof a mold cavity. For example, a mat of felted 'glass ibersor the likemay be convolutely wound into a cylindrical body l@ on a form or core 11and inserted in a cylindrical mold casing 12, as indicated in Figures 1and 2.

The form or core 11 is then withdrawn to leave the mold' casing 12 linedwith the convolutely wound fiber matting it), more fully illustrated inthe aforementioned copending Randolph application. The cylindrical moldcasing 1.2 is provided with end flanges 13 which are adapted to closeagainst cooperating iianges or other mold closure members to bedescribed below. I

When making a closed-end tank, fiber matting pieces in the shape of endwall caps 16 and l1'7, which may be identical except that the upper capv16 has a central hole formed therein, are also provided. The caps 16and 17 may be shaped by conventional means which will be known to ythosefamiliar with the fabrication of fiberreinforced molded articles. Forexampie, bers may be blown over cup-shaped screens to form a cup-shapedmat, also more fully illustrated in the aforementioned copendingRandolph application, and a resin adhesive may be'sprayed as a lightcoating on the lbers as they `accumulate on the screen to hold the fibermat together during subsequent handling. The outer ldiameter of the caps16 and 17 may be equal to the internal diameter of the convoluted mat 10whenit is lpositioned within the casing 12.

Upper and lower mold caps Z0 and 21 are provided for closing the moldand shaping the end walls of a tank formed' therein. Suitable anges onthese caps are adapted to close againstthe end iianges 13 of thecylindrical mold casing 12. r[he internal surfaces of the casing capsare in the shape of oblate ellipsoids of revolution, or they may behemispherical.Vr Theymay also have other shapes which, however, will beless adaptable to the production of a strong tank structure. This isimportant inasmuch fas applications to which the invention relates mustusually be capable of withstanding pressures in excess of 500 p.s.i. andpressures up to 1000 p.s.i. or higher may be required. The inner surfaceof theupper casing cap 20 is centrally relieved as at Z5 and is providedwith a central annular rib 22 and with vent sleeves or passages 23. Theflange of the upper casingcap is provided with a suitable sealing ring24. The lower casing cap 21 is provided with a central resin supply line26. A deep annular groove 27 is formed around the lower casing cap. ApluralityV of drains or sprues 28 open downwardly from .the bottomof theannular groove 27. 'The flange associated with the lower casing cap isprovided with a A flexible envelope is provided for expansion againstthe ber lining. An orifice structureassociated with this envelope isadapted to be'inserted upwardly through the central opening in the upperfiber capito and through a central opening in the easing cap 20,radially inwardly of the annular rib 22.1 The flexible envelope'rnaycomprise a rubber bag 3@ encased in a protective sheath of polyvinylacetate lm, or cellophane film, or similar material which will protectthe molding materials against chemical action of vulcanizing agents orresidues thereof associated with the bag 30. The bag 30 and protectivesheath 31 are supported on a flanged and threaded neck 32 and are sealedthereto by suitable washers and gaskets 33 which are clamped bytightening of nut 35 threadedly engaged on the outer end of the neck 32.When lled,

but not dilated, the bag preferably has a volume approximately equal tothe diierence between the volume of the chamber dened lby the casingmembers 12, 20 and 21 Iand the volume occupied byy the mats 10, 16 and17. l

There are also provided round rings of ber matting 40 of progressivelyvarying sizes, which may be stitched together for convenienceinhandling, as shown at 41 in Figure 3. y

Prior to the molding openation, the convolutely wound ber matting 10 isinserted in the cylindrical casing 12 as above described. The ber caps16 and 17 are then telescoped within the ends of the convolutely woundmatting yas indicated in Figures 3 and 4. A group of rings 4i) is tackedaround the central opening of the upper ber cap 16 las indicated inFigure 3. The annular groove 27 in the lower cap 21 is stuffed with beras indicated in Figure 4. Thereupon, the casing members are closedtogether, and air or other gas is introduced into the envelopecomprising the bag 30 to inate it just enough to bring it into contactover its entire outer surface with the inner surface of the layed-upform of ber matting.

At this point (when using liquid rather than gas to iniate the bag 30)it had previously been the practice to introduce liquid resin into themold for impregnating the ber matting. Instead, it is now preferred tocontinue introducing gas into the bag at a moderate rate until theinterior gas pressure has been gradually raised to 25-30 p.s.i. or more,and then to relieve this pressure down to a relatively low value of`about 5 to l0 p.s.i. before introducing the liquid resin. The purposeof this is to pre-compress the ber matting as much as possible and, atthis stage, to produce as much shifting or adjustment of the bers as maybe necessary for the initially separate mat portions to slide relativeto one another in their regions of overlap in accommodating themselvesto the contour of the mold sections while being so compressed This seemsto accomplish a minor, but nonetheless important, controlledredistribution Vor adjustment of the bers in those regions of overlap,forcing the bers more rmly into contact with the mold along thejunctures i2 between the interior side and end walls of the mold wherethere are Iabrupt'. changes in the mold contours. It also seems to ausean interlocking of the bers from opposite sides ofthe initial lap seams50 between the side wall mat llt) and the end caps 16 and 17 so as tovirtually obliterate or eliminate all trace of the seams 5i) the seamsthat further uncontrolled migration of the v mat portions on oppositesides of the seams after 'the liquid resin has been introduced iseiectivelyk eliminated.

Previously, this tendency toward uncontrolled migrationr of bers in theregions of the seams 50,'iafter introducing y and the mold chamber morenearly vertically disposed than horizontally (preferably vertical asshown), `arrieasured amountof resin `45 is then introduced throughk thesupply line 26. The `amount of resin introduced is such that the chargewill permeate the entire ber lining during a subsequent compressingoperation. Preferably, a siight excess of resin is provided. Theintroduction of a large excess of resin at this point is permissible butunnecessary, since it is subsequently expressed out of the mold duringnal compressing of the ber matting before lsetting the resin.

The resin comprises any suitable thremosetting resin adapted to be setat temperatures above room temperature. It is preferred that a resin beemployed that will set at about 200220 F. Resins adaptable to thepurposes herein described are well known to the art, and in general,high-temperature-resistant thermosetting resins of the type .usuallyknown as polyester resins, such as epoxy resins or styrene-phthalicanhydride condensation pro-ducts, may be employed together with suitablesetting agents adapted to control setting temperature, all as is wellknown in the art.

As the resin is introduced into the bottom of the molding chamber, theupper vents 23 and -lower drains 28 are open. As the resin rises aroundthe bag 30, it forces air within the ber matting out through both thelupper vents 23 and lower drains 28 until the resin flows into theannular groove 27 and out through the lower drains. Thereupon the lowerdrains are plugged as shown in Figure 5 and the introduction of resin iscontinued. The rising column of resin displaces the air above it andcontinues to force it out of the upper vents 23, but at no time is theber lining wetted with resin ahead of the path of escaping air. Theabove prescribed air pressure within the bag 3i) is sufciently high toprevent billowingof the bag at the lower corners thereof or elsewhereand to thereby further restrain the bersfrom migrating up wardly withthe rising resin by maintaining firm contact of the envelope with thematting over the entire inner surface of the ber lining. Such migrationtendency is also reducedl by the precompression of the Vbers before theresin is introduced, as explained above.

As hereinbefore noted, the liquid resin acts as a lubricant for thematted bers. ySuch lubrication not only produces the previouslytroublesome tendency toward migration of the bers, but it also rendersthe bers more susceptible to further compaction due to the pressure inthe bag 3G. This latter effect is illustrated in Figure 6 with someexaggeration byl showing the level L to which liquid resin has beenintroduced into the ber mass,1 the ber body below the level.L where thefibers have been permeated and lubricated being compressedV more thanabove the level L where-the resin has not yet contacted the bers. Thistransition zone rises as the level L is raised in the next step of theinvention.

Additional pressure is now applied by slowly feeding additional gas intothe flexible envelope comprising the bag 3i) to cause substantialfurther compressionvof the ber lining within the molding chamber andprogressive reduction of its thickness. For example, a 1A; inch ber wallmay be compressed to a final thickness of approximately 3%[6 inch. Dueto the resultant diminution of the 'volume of the berlining, the resin45 is expressed upwardly throughout the entire ber lining. There ispreferably a slight excess of resin which is expressed outwardly throughthe upper vents 23, thus signalling that impregnation of the entire berlining is complete. i

In some applications the above forming steps may be sufficient; however,inv most applications it is preferred toV complete V'final compressionby removing plugs or caps from thedrains or spruesZS, which hadheretofore been closed, and'thereupon slowly injecting additional gasinto the` bag to applyan additional and ultimate compressing pressure tothe gas within the bag 30 to express additional excess -resin both fromthe `lvents 23 and through the kdrains orspruesj28. Thisultirnatepressure is selected to produce the desired final wall thickness anddesired final compaction of the fibers.

As previously indicated, one of the objectives of the invention is tominimize the entrainment of air in the resin with which the fiber bodyis impregnated. For this purpose, it has been found to be beneficial tosubject the liquid resin to a de-aerating step before introducing itinto the fiber body. The liquid resins of commerce contain relativelylarge quantities of air dispersed therein, some of it apparently beingdissolved and some being merely nely dispersed as microscopic bubbleswhich may give only a slightly turbid appearance to an otherwise clearresin.

Such de-aerating may be performed by simply applying a vacuum above theresin in a suitable container until the entrained air has been largelydrawn out of the resin. This produces a profusion of small bubbles inthe body of the liquid resin, which bubbles rise rapidly to the surfaceand burst. A vacuum of 25 to 28 inches of mercury is highly effectivefor this purpose.

Once the resin has been de-aerated, it may be briey exposed again to airor other gas for forcing the resin4 from the same container into themold as described above without taking on any significant amount ofadditional air. AIf desired, however, any other procedures may beemployed for lprotecting the de-aerated resin from contact with air orother gases While it is being forced into the mold.

A related objective of the invention, as noted above, is to moreeffectively eliminate air contained in the interstitial spaces of thefiber matting prior to its permeation with the resin. This may be donewithout first de-aerating the resin but, preferably, is done inconjunction therewith by evacu'atng the mold cavity through any suitableconnection in the mold cap 20, such as an additional vent sleeve 23,while the others are suitably closed or capped and while the resinsupply line 26 is connected through any suitable, valved conduit (notshown) to the bottom of the resin de-aerating container. `By openingthis valved conduit to flow of resin therethrough, the lresin may bedrawn into the mold in the desired amount by the vacuum in the mold,either by admitting air slowly into the top of the resin container toprovide the necessary pressure differential or by gradually applyingpressure to the resin in the resin container by any desired mechanicalmeans, such as a piston, without exposing it to air or other gas.Obviously, drawing of the resin into the mold by vacuum, as described,will also draw dispsersed gas `from the resin if the resin has notpreviously been de-aerated, or Will draw additional dispersed gastherefrom in an amount depending upon the degree of vacuum created inthe mold and the extent to which the resin may have been previouslyde-aerated. When the resin flow has been stopped, the resin in the moldmay be expressed throughout the upper portion of the ber body as beforeby the application of such pressure to the bag 30 as is needed for thatpurpose. Complete permeation of the fiber body may be detected, forexample, when the resin has been expressed into the vacuum line throughthe uppermost vent sleeve 23 until it is visible in a transparent glasstrap or the like (not shown) which may be provided in the vacuum linefor that purpose. Thereupon, the vacuum line is disconnected from thesleeve 23 so that it is left open, and, optionally, the drains or sprues28 are also opened in order to permit excess resin to be expressed outof the mold as the pressure in the bag 36 is raised to the desired nalcompressing pressure.

After the fiber body of the article has been thus impregnated and shapedwithin the mold, and while the shape is maintained by pressure from theenvelope 3i), the casing of the mold is subjected to heat in order toset the resin. Heating elements or heating coils (not shown) ofconventional structure are provided adjacent the mold casing members,preferably in such a manner that uniform heating over` all mold surfacesis achieved to as' great a degree as possible, in a manner which will Ibe familiar to those skilled in the art. Preferably, during heating ofthe mold and setting of the resin, the various vents 23 and drains orsprues 2S are plugged or capped.

After setting of the resin, the bag 3@ is'opened to the atmosphere topermit it to collapse and be withdrawn through the mouth or throat inthe upper end of the formed article. For this purpose, the nut 35 may beturned off from the bag neck 32 and the casing cap 20 may be releasedfrom the casing l2 and removed The lower casing cap 21 may then also bereleased from the casing 12 and removed, and the iinished molded articlemay be slid longitudinally out of the casing 12.

It will be noted that the initial seams 5@ between the fiber caps andthe cylindrical fiber wall extend as taperedlap seams across the cornersor junctures between the end cap portions of the final product and thecylindrical side wall portions of the final product, and that theseseams are permeated by a homogenous body of set resin to form an overallintegral body. The matted fiber elements initially brought together onopposite sides of these seams have numerous outwardly projecting ends,and compression of the fiber body in the course of the above describedsteps causes considerable migration of the individual fibers throughoutthe ber body. As previously explained, the result is that the finallyset body is substantially homogenous, and, as a general rule, virtuallyno trace of the lap seams is detectable in crosssections cut throughthese regions of the final product. The tapered-lap seams, by providingrelatively large seam areas for interlocking of fibers and foradjustment of the fiber mats within the mold, contribute to theobtainment of this result.

During the final compressing operation, it is desirable that the gasforced into the bag 3@ be supplied at a slow and, preferably, aconstantly diminishing rate. A suitable adjustable air pressureregulator of any conventional type (not shown) may be provided in thepressure line to the bag Sil to closely control the increase in pressureby throttling the flow of gas into the bag 3i). The rate of increase ofthe air pressure is preferably slower and slower as maximum compressingpressure is approached. ln a typical application, an utilmate pressuredifferential between the inside of the bag Si) and the surroundingimpregnated fibers may be of the order of 25 or 30 p.s.i., althoughhigher or lower pressure differentials may be desired in different jobs.

' During the application of heat to set the resin, the final pressureAexerted by the Vbag Si) is preferably held substantially constant, andany drop in this pressure is particularly to be avoided, in order toinsure that the impregnated mass remains immobile until curing of theresin has been completed. This requires that steps be taken tocompensate for expansion of the gas in the bag as it absorbs heat duringthe setting of the resin. Such heat cornes both from the externalheating of the mold and from the exothermic setting reaction of theresin, which will generally raise the resin temperature above thetemperature of the externally heated mold. The maximum resin temperatureis generally reached and some subsequent cooling generally occurs beforethe resin is fully set, thus tending to cause contraction of the gas inthe envelope 30 and reduction of the pressure exerted thereby while theresin is still in a pliable state. A slow increase in pressure, withinlimits, while the temperature in the bag is rising would not alone produce serious results. However, a subsequent decrease in pressure, due toa temperature drop before the resin is fully set, is apt to permitexpansion of the compacted bers so as to cause what .might be looselytermed a delamination of the liber and resin mass, leaving undesiredvoids and weak areas in the wall of the inished tank.

Thus, it is` desirable during the resin curing step to "Q maintain a-substantially constant pressure differential between the inside and;outside of the bag 30. This may readily be done in various Way, as willbe apparent to those skilled in the art. For example, using any sourceof relatively high, positive air pressure to maintain a predetermined,somewhat lower, final compressing pressure in the envelope, the pressureregulator mentioned above may be used in the supply line to keep theinternal bag pressure up tothe predetermined value While the temperaturein the bag is falling; and, if desired, a conventional pressure reliefvalve (not shown) may be used in the same supply line between thepressure regulator and the bag for releasing gas from the bag in theevent the pressure therein should rise excessively With increasingtemperature during Ithe resin curing operation.

When producing tanks in accordance with the procedures described andutilizing a final effective pressure in the bag 30 of 25 to 30 p,s.i.,while the plugs Z8 are removed and the passages 23 are also open, bothbefore and during the setting of the impregnating liquid, substantialcompression of the original liber matting and discharge of excess resinoccur. By reason 'of the lubrication of the loose fibers by the liquidimpregnating Yresin While this pressure exists, the compaction of thefibers and discharge of excess resin are greatly facilitated, and

a fiber content of about 40% to 50% by volume of the final tank bodyinherently results. By contrast, when fiber mats are preimpregnated withresin and the resin has been partially cured at normal pressures inaccordance with certain practices in the art, after which theimpregnated mats are shaped in a mold and subjected to heat and pressureto finish the curing of the resin, it is virtuallyimpossible to obtainber contents in the finished product as high as 40%. Tanks formed withlower liber contents are weaker in direct proportion to the differencein liber content, other factors remaining the same. Therefore, the Vhighliber content of the tanks produced in accordanceV with the presentinvention is believed to be an important result of the invention.

Figures 6 and 7 are intended to illustrate, somewhatL schematically,certain steps in the manufacture of articles according to the invention.fFigure 6' shows `apparatus employed in the invention prior to the finalcompressing or forming step. The fiber'lining is moderately compressed,andthe level L ofthe resin `45 may be slightly above the half-way heightof the molding chamber at the conclusion of feed. Figure 7 shows thesame apparatus and the fully 'impregnatedv lining subsequent to thefinal compressing or forming step and just prior to the step of'heatsetting theformed article( n Thevvarious fiber mattings and caps willmestl advantageously comprise glass fiber, due to the high strengthproperties of these fibers. The service life of articles formed inaccordance with the general objects of the present invention can beVfurther improved by yforming 'each of such mattings and caps with aninner layeror lining of other types ofV fibers, such asacrylic fibers,for

example, a copolymer of vinyl chloride andv acrylonitrile formed asrelatively line fibers. viin practice, the cylindrical body of iibermatting 10 shown in Figures land `2 may be made by iirst rollingjone ormore layers of 'one or more layers of iibers vof another type.

fiber elements Aadjacent theends of the tank, the fibers at fibers ofVone type on the core 1i., followed by rolling the contiguousfsurfacesof each winding merge or migrate into one another acrossl the severalwinding interfaces. Thus, all of these interfacesvir'tually disappearinthe final steps of the prccess, and the transition from Lfibers of onetype to fibers of the Other'type is a gradual one,'

no sudden change from fibers of one typek to iibens of another beingdiscernible and the Yfibers of the two types product from one typeroffiber `tothe other isa gradual transition. As a result, except for sucha gradual transition in the chemical composition and'physical propertiesof the fibers between :the inner and outerv surfaces of the finishedproduct, the body of the tanks is not only seamless throughout but` issubstantiallyk homogeneous throughout. jin thejappended-claims, theterms seamless and homogeneous are used in this sense.

As more fully expl-ained in another applicationr of Donald W. Randolph,Serial No. 704,028, filed December 20, i957, other desirable features oftanks made in accordance with the present invention are that thetaperedlap seams S0 between the cylindrical side wallmatting 10 and theend wall mattings 16 and 17 extend around and radially inwardlyalongithe end walls to prevent excessive creeping of the matting in theside wall, and the foot structure joins the bottom Wall of the tank at acircular zone that is concentric with the side Wall, is ofvsubstantially smaller diameter than the side wall, and is spacedradially inwardly from the side wall a sub stantial distance.

Turning now to Figunes 9-Al2, certain modifications of the invention areillustrated `as Vapplied to the production of open end, hollowcylindrical bodies, such as lengths of tubing. In general, the procedurefor producing such bodies is similar to the procedure just described formaking Aclosed end tanks, but with certain variations, some 4of whichare also applicable to the production of closed end tanks as will lbeapparent to those skilled in the art.

`As shown in FigureV 9, a cylindrical form of' fiber matting, generallydesignated 60 may be wound ,on the same core lll shown in Figure 2. Inthis case, however, in order to secure greater tensile strength in thecom- Iposite cylindrical wall material of the final product, the form offiber matting may be made up `of one or more ,turns of felted glassfiber matting forming an inner felted layer 61, one or more turns of anyconventional, Woven, glass ber fabric forming an intermediate layer62,and one or more turns ofthe felted glass fiber matting forming lan outerfelted layer 63. The greater tensile strength thatcan be built into Vasuitable woven glass fabric, comfpared to the strength of av feltedglasstiber matting, adds kgreatly to the tensile strength of thefinished resin impregnated material. l

Obviously,l any :desired arrangement /offelted and woven,knitted, or-nettedrfabnic layers, or felted matting only,orother fabrics only, maybe used without d-eparting from the Scope of the invention as claimedherein. However, there are distinct practical and economic advantages tothe use of felted iiber matting to the extent that the requisitestrength of the'finished product for a given Wall thickness will permit.The felted iiber matting, of course, is less expensive. vIn-'addition,itis more rigid more securely hold the separate mat sections againstrelative movement and so as Vto produce `a morefnearlyv homogeneousproduct in the regions of overlap. lln ad dition, the .multiple filamentthreads of which woven fabrics and the like are made are porous -to adegree and contain some air,` but these threads'per se are not readilypermeated with liquid resin. The greater,y permeability of feltedfibermatting facilitates the iiow. of liquid resin about each individualfilament so as to more completely .impregnater the liber body and drivethe therefrom.

\When forming tubingas` illustratedl in {Figures 9-12,

the felted ber mat-tinglayers el and 63 may advantageY I ously projectsomewhat beyond'eac'h end of the cylinv nrical mold andy be foldedradiallyv inwardly when closing the ends of fthe mold, as Lhereinafterdescribed. The weven .fabric .layer 62A, onf the other hand, may-haveenvases more stable, better defined dimensions so that it may be made ina width more closely corresponding to the axial length of the mold andmay be more accurately wrapped on the core l1 with little or noirregularities at each end of the mold. If desired, an inner layer, oran outer layer, or both (not shown) of thin, preimpregnated and cured,glass ber, surfacing mat may also be ,wrapped aboutA the core lll toprovide smoother nished surfaces on the final article or to aid inholding an inner and/or outer layer of woven fabric in place, if such anarrangement of matting materials is desired.

The core 11, withthe matting layers 61, 62, and 63 wrapped thereon isshown in Figure 9 after this assembly has been inserted in a cylindricalmold 65, similar to the mold section 12 of Figure 2. The core 11 is thenslid out to leave the porous form in place in the mold. Thereupon, abottom mold closure plate 66, and a top mold closure plate 67 havingAthe same flexible bag 31 of Figure 4 similarly mounted thereon, arepositioned to close the mold as shown in Figure 12 while folding theedges rof Vthe felted ber layers 61 and 63 radially inwardly. Theclosure plates 66 and 67 are suitably clamped in place against gaskets68 to securely seal the mold.

As shownin Figures 10, 11 and l2, the top closure plate 67 is providedwith a central aperture 71 to receive the neck 32 of the bag 31 by whichthe bag is inflated after closing the mold. The top closure plate 67 isalso provided with a pair of diarnetrically opposed vents or sprues 72and 73 positioned for axial alignment with the ber form in the mold toexhaust air and, nally, to exhaust excess resin therefrom. The bottomclosure plate 66 is preferably provided with four vents or spines 74,75, 76, and 77, similarly located for also exhausting excess resinduring nal compression of the completely impregnated ber form. Thebottom plate is also provided with a central inlet tube 78 forintroducing liquid resin into the mold.

When the mold has been closed about the ber form and about the bag 31,as shown in Figure l2, the impregnating and molding operations may beperformed in the same manner as in making closed end tanks according toFigures l-7, except that the bottom vents 74, 75, 76, and 77 may beinitially closed by suitable plugs (not shown) before introducing resinthrough the inlet tube 78. These vents 74, 75, 76 and '77 may remainclosed until the resin has been expressed throughout the ber form andsome excess resin has been forced out of the top vents 72 and 73 byincreasing the gas pressure in the bag 31. Thereupon, the vents '74, 75,76, and '77 may be unplugged and remain open while the bag pressure isbeing raised to the ual compressing pressure. As in making closed endtanks, all six of the vents '72, 73, 74, 75, 76 and 77 are preferablyclosed before applying heat to the mold to set the resin.

When the molding and resin curing operations are completed and themolded tube has been removed from the mold, it is a finished articleexcept for the necessity for cropping oli the irregular extremities ofthe tube. Obviously, the tube may be cut up into any shorter lengthswhich may be desired.

The above described examples of the invention may be varied withoutdeparting yfrom the scope of the invention. For example, the centralmold casing and the central portion of the tank need not necessarily becircular in cross-section, although generally a central portion oftubular shape is preferable; Also, the foot structure of the tank maytake any of a variety of forms. Other possible modifications of thedetails of the invention as disclosed herein will suggest themselves.The invention is not limited to all such details, but is defined by therfollowing appended claims.

What is claimed is: l. A method of forming a hollow, ber-reinforced,molded article, comprising the steps of providing a substantially closedrigid molding chamber lined with porous and compressible ber mattingthat includes at least one layer of unwoven loosely felted bers,expanding a flexibleenvelope disposed within said chamber into contactwith'said ber matting, and creating a relatively high pressurediiferential between the insideand outside of said envelope suiiicientto compress and compact said ber matting and force it to conform to themold in rm contact therewith, then reducing said pressure diierential toa relatively low value to facilitate permeation ot the ber matting withliquid resin and investing a thermosetting liquid resin into the chamberin permeating relationship with at least a part of said ber matting,slowly increasing said pressure differential to a nal high valuesuicient to gradually further compress said ber matting while ventingsaid molding chamber until gas therein and some excess resin areexpressed through said Venting from said chamber, and then applying heatto set the resin in permeating relationship with the ber matting to forma substantially homogeneous, molded, hollow body of ber-reinforcedsolidied resin.

2. A method of forming a hollow, ber-reinforced, molded article,comprising the steps of providing a substantially closed rigid moldingchamber lined with porous and compressible ber matting that includes atleast one layer of unwoven loosely felted bers, expandin-g a flexibleenvelope disposed within said chamber into contact with said bermatting, and creating a relatively high pressure differential betweenthe inside and outside 0f said envelope suicient to compress and compactsaid ber matting Vand force it to conform to the mold in rm contacttherewith, then reducing said pressure differential to a relatively lowvalue to facilitate permeation of the ber matting with liquid resin andinvesting a thermosetting liquid resin into the chamber in permeatingrelationship with at least a part of said ber matting, slowly increasingsaid pressure dilerential to a iinal high value suicient to graduallyfurther compress said ber matting while venting said molding chamberuntil gas therein and some excess resin are expressed through saidventing from said chamber, and then applying heat to set the resin inpermeating relationship with the ber matting while maintaining said inalhigh pressure to form a substantially homogeneous molded body ofber-reinforced solidied resin.

3. A method of forming a substantially closed, hollow, ber-reinforced,molded article having a cylindrical side wall, end walls, and an openingin one of said end walls, comprising providing a hollow rigid mold thatdenes a substantially closed cavity of corresponding' shape anddimensions lined with a plurality of overlapped sections of preformed,porous, ber matting over its entire interior surface except for the areaof said end wall opening to form a ber lining, each of said sections ofber matting including at least one 'layer of unwoven loosely feltedbers, providing a exible envelope inside said ber liningand a iillingconduit for the envelope communicating therewith and with the exteriorof said mold through the area of said end wall opening, inating saidenvelope within said chamber into contact with said ber lining byintroducing gas into the envelope through said lling conduit at apressure in excess of that surrounding the envelope in said chamber,increasing the gas pressure in said envelope until a relatively highpressure diierental is created that is suicient to compressV and compactsaid ber lining and Yforce it to conform to the mold in rm contacttherewith, then relieving said pressure differential to a relativelyYlow value to facilitate permeation of the ber lining with liquid resinand investing a measured amount of a thermosetting liquid resin into thechamber in permeating relationship with a part only of said ber lining,slowly increasing the pressure of gas in said envelope to furthercompress said ber lining while venting said chamber until a nal pressuredifferential is created on opposite sides of said envelope ofsuflicient'magnitude to express from the chamber any gas therein and atleast 13 some excess resin, and then applying heat to set the resin inpermeating relationship with the ber lining while maintaining said nalpressure differential to form a substantially homogeneous molded body ofber-reinforced solidified resin.

4. A method of forming a hollow, ber-reinforced, molded article,comprising the steps of providing a substantially closed rigid moldingchamber lined with porous and compressible ber matting that includes atleast one layer of unwoven loosely felted bers, expanding a gas filledflexible envelope within said chamber into pressure contact with saidber matting, creating a relatively high pressure differential betweenthe inside and outside of Y said envelope sufficient `to compress andcompact said ber matting and force it to conform to the mold in firmcontact therewith, then relieving said pressure differential to arelatively low value and investing a thermosetting liquid resin into thechamber in permeating relationship with at least a part of said bermatting, slowly increasing said pressure differential to a nal highvalue While venting said chamber to gradually compress the ber mattingand insure that said liquid resin is expressed throughout the same inpermeating relationship therewith and that any gas therein and excessresin are expressed through said venting from said chamber, and thenclosing said venting and applying heat to set the resin in permeatingrelationship with the fiber matting to form a substantially homogeneousmolded body of ber-reinforced solidied resin.

5. A method of forming a hollow, ber-reinforced, molded article,comprising the steps of providing a substantially closed rigid moldingchamber lined with a cylindrical form of porous and compressible bermatting to form a ber lining that includes at least one layer of unwovenloosely felted fibers, expanding a gas filled flexible envelope withinsaid chamber into contact with said ber lining, creating a substantialpressure differential between a relatively high gas pressure within saidenvelope and a relatively low gas pressure in said ber lining toinitially compress the same against the molding chamber walls, relievingsaid pressure differential to a relatively the same in permeatingrelationship therewith and to exv hollow body of ber-reinforced solidiedresin.

low value and then investing a hardenable liquid resin n into thechamber in permeating relationship with at least a part of said berlining, while venting said chamber, slowly increasing said pressuredifferential to a nal high value While still venting said chamber tofurther compress said ber lining and insure that said liquid resin isexpressed throughout the same in permeating relationship therewith andair and excess resin are expressed through said venting from saidchamber, and then, While maintaining said nal high pressure differentialsetting said resin to a hardened state in permeating relationship withthe ber lining to form a substantially homogeneous, molded, hollow bodyof 'ber-reinforced solidied resin. v l

6. A method of forming a hollow, ber-reinforced, molded article,comprising the steps of providing a substantially closed, rigid, moldingchamber lined with a porous and compressible mat comprisingunwovenloosely felted bers, expanding a gas filled flexible envelopewithin said chamber into contact with said mat, creating a substantialpressure differential between a relatively high gas pressure within saidenvelope and a relatively low gas pressure in said mat sufficient toinitially compress and compact the same and force it to conform to themold in firm contact therewith, reducing said pressure differential to arelatively low value to facilitate permeation of the ber mat with liquidresin, investing a hardi enable liquid resin into the chamber inpermeating relationship with at least apart of said mat, slowlyincreasing said pressure differential to a nal high value while ventingsaid chamber to further compress said mat and insure that said liquidresin is expressed throughout 7. In the method of makingfiber-reinforced resin articles, wherein porous ber matting is disposedbetween a vented mold surface and a flexible membrance and is' held inplace against the mold surface by a pressure differential created onopposite sides of the membrance while introducing a settable liquidresin into a part of the ber matting, and wherein said pressuredifferential is then increased to force gas from the matting and topermeate the pores thereof with resin by expressing the resin throughoutthe matting, the step of de-aerating the resin by subjecting it to avacuum of the order of at least 25 inches of mercury before introducingit into the ber matting.

8. In the method of making ber-reinforced resin articles, wherein porousber matting is disposed between a vented mold surface and a flexiblemembrance and is held in place against the mold surface by a pressuredifferential created on opposite sides of the membrance Whileintroducing a settable liquid resin into a part of the ber matting, andwherein said pressure differential is then increased to force gas fromthe matting and t0 permeate the pores thereof with resin by expressingthe resin throughout the matting, the steps of reducing the pressure inthe ber matting between the mold surface and the flexible membrane tocreate a vacuum therein for de-aerating the ber matting and the liquidresin While drawing the resin into the matting, and finally increasingsaid pressure differential sufficiently to express the resin throughoutthe matting.

9. In the method of making fiber-reinforced resin articles, whereinporous ber matting is disposed between a vented mold surface and aflexible membrance and is held in place against the mold surface by apressure differential created on opposite sides ofl the membrane Whileintroducing a settable liquid resin to a part of the ber matting, andwherein said pressure differential is then increased to force gas fromthe matting and to permeate the pores thereof with resin by expressingthe resin4 the resin throughout the matting.

References Cited in the le of this patent UNITED STATES PATENTS OTHERREFERENCES Vacuum Deposition on Thin Films-The Degassng of PlasticMaterial in Vacuo-chap. 2, pages 44-69. L. Holland, 1956.

1. A METHOD OF FORMING A HOLLOW, FIBER-REINFORCED, MOLDED ARTICLE,COMPRISING THE STEPS OF PROVIDING A SUBSTANTIALLY CLOSED RIGID MOLDINGCHAMBER LINED WITH POROUS AND COMPRESSIBLE FIBER MATTING THAT INCLUDESAT LEAST ONE LAYER OF UNWOVEN LOOSELY FELTED FIBERS, EXPANDING AFLEXIBLE ENVELOPE DISPOSED WITHIN SAID CHAMBER INTO CONTACT WITH SAIDFIBER MATTING, AND CREATING A RELATIVELY HIGH PRESSURE DIFFERENTIALBETWEEN THE INSIDE AND OUTSIDE OF SAID ENVELOPE SUFFICIENT TO COMPRESSAND COMPACT SAID FIBER MATTING AND FORCE IT TO CONFORM TO THE MOLD INFIRM CONTACT THEREWITH, THEN REDUCING SAID PRESSURE DIFFERENTIAL TO ARELATIVELY LOW VALUE TO FACILITATE PERMEATION OF THE FIBER MATTING WITHLIQUID RESIN AND INVESTING A THERMOSETTING LIQUID RESIN INTO THE CHAMBERIN PERMEATING RELATIONSHIP WITH AT LEAST A PART OF SAID FIBER MATTING,SLOWLY INCREASING SAID PRESSURE DIFFERENTIAL TO A FINAL HIGH VALUESUFFICIENT TO GRADUALLY FURTHER COMPRESS SAID FIBER MATTING WHILEVENTING SAID MOLDING CHAMBER UNTIL GAS THEREIN AND SOME EXCESS RESIN AREEXPRESSED THROUGH SAID VENTING FROM SAID CHAMBER, AND THEN APPLYING HEATTO SET THE RESIN IN PERMEATING RELATIONSHIP WITH THE FIBER